Heart rate variability and underlying cardiovascular performance during spontaneous and controlled breathing

The autonomic nervous system plays an important role in modulating cardiovascular function. Previous studies have shown that impairment of the autonomic regulation is a marker of cardiovascular diseases, but none has simultaneously quantified underlying cardiac and vascular changes. We hypothesized that by tracking multiple variables underlying autonomic control, performance of the heart and the vascular system, a more comprehensive view of cardiovascular regulation can be obtained. The protocol involved five minutes of spontaneous breathing, followed by five minutes of intermittent breathing on experimental subjects free from existing cardiac and respiratory ailments (n=7, males 25-38 years-old). Time and frequency domain heart rate variability (HRV) analyses were performed to probe overall cardiovascular regulation during the two breathing patterns. Rate pressure product (RPP) to assess cardiac performance and estimates of arterial compliance (C) to assess vascular function were also obtained. Time domain results showed dissimilar variations in heart rate between the two breathing patterns (p < 0.01). A shift in power from high frequency components to low frequency components was observed in the power spectrum which indicates a shift from parasympathetic to sympathetic activity. Differences in RPP for the two breathing patterns were not significantly significant, indicating overall myocardial oxygen consumption was unaffected by the controlled breathing protocol. However, components contributing to RPP, i.e. mean HR and systolic blood pressure, both slightly increased during intermittent breathing. Variations in beat to beat arterial compliance showed that compliance increased during breath holding and decreased during release, but mean beat to beat arterial compliance values of the two breathing patterns was not statistically different. Thus, we were able to track multiple variables underlying autonomic control, cardiac performance and vascular function. We conclude that that short-term perturbation in controlled breathing can provide an effective means to probe overall cardiovascular regulation. In normal subjects, such perturbations affect primarily autonomic control and less so in affecting energy consumption of the heart or vascular function.